Type 1 diabetes mellitus is one of the leading chronic conditions among children and youth and its impact is increasing worldwide. Intense medical and nutritional management of the diabetic condition and any existing cardiovascular disease (CVD) risk factors is currently the key treatment approach. Yet even under rigorous adherence to these regimens, the onset of diabetes in childhood places this population at significantly increased long term risks of CVD morbidity and mortality. Research has shown that adults with diabetes are more susceptible than nondiabetics for increased CVD morbidity and mortality associated with exposures to outdoor air pollution. Very little research in this area has been conducted to examine whether children and youth with diabetes are similarly susceptible; however the inference seems reasonable, given that children typically spend more time outside and are more sensitive to environmental exposures. Since the early onset of type 1 diabetes increases CVD risks in adulthood, there is an urgent need to understand the role of air pollution exposures in this population. With representation of diverse racial and ethnic groups and geographically distinct areas of the US, as well as the availability of extensive, existing information on CVD risk factors, the SEARCH for Diabetes in Youth Study (SEARCH) offers an unprecedented opportunity to systematically study, in an efficient manner, the short and long-term effects of air pollution on cardiovascular risk. In this high-risk population of youth, we will examine the acute effects of air pollution exposures on inflammatory markers and measures of cardiovascular function, as well as the chronic effects of these exposures on cardiovascular structure. Understanding the role of air pollution on inflammation and subclinical CVD among children and youth with type 1 diabetes could have a major impact on treatment approaches and behavioral recommendations.